This invention relates generally to irrigation control systems, and, more particularly, to such systems used to control a relatively large number of irrigation or sprinkler valves in accordance with one or more desired schedules of operation.
Large irrigation systems, whether used to irrigate agricultural property, sports facilities, or other types of terrain, include a relatively large number of water valves, which are typically solenoid operated, and which must be opened and closed in a desired and controllable sequence of operations, as dictated by the terrain, weather conditions, crop or turf characteristics, and other factors. For many years, such large irrigation systems have been controlled by means of a central electromechanical controller which operates in a sequential fashion, i.e., one valve or group of valves is switched on for a preselected watering time, then the next group is switched on for another preselected watering time, and so on until the schedule of operations is completed. Typically, such electromechanical controllers include a timing motor and a plurality of switches for selecting the watering times. Such controllers are usually limited to only one or two different schedules of operations. Although this limitation imposes no significant hardship on some users of large irrigation systems, agricultural users in particular need a control system which can be conveniently modified or reprogrammed to accommodate crop changes as well as changes in climatic conditions. Changing the watering schedules of electromechanical controllers is not only time consuming, but also can result in unnecessary waste of water, before the need for a change becomes apparent, and as the new schedule is being brought into use. Moreover, when the old schedule is needed again it has to be regenerated.
Ideally, a large irrigation control system should be capable of executing several different schedules, concurrently if desired, and the user should be able to add, delete, or modify schedules without disturbing the operation of the system. Moreover, it should be possible to so modify the schedules using a "language" of control instructions which have significance to the irrigation user, and the instructions should not be limited to the sequential mode of operation of conventional electromechanical controllers. Furthermore, an ideal irrigation control system of this kind should be inherently reliable. Control systems of the prior art typically transmit control signals to switch valves on or off at the times when they are designated to be switched on or off. However, transmission of a control signal to switch a valve on or off provides no assurance that the valve has been actually switched in the desired manner, and will remain in the intended condition. Such prior art systems frequently fail to operate as intended when a valve does not respond to a control signal or fails to remain in its switched condition.
Accordingly, there has long been a need for an irrigation control system which fulfills the foregoing ideal requirements and overcomes the shortcomings of the prior art. The present invention is directed to this end.